Gear shift device

ABSTRACT

A gear shift device for a vehicle with a manually operated gearbox ( 30 ) and a gear shift device ( 10 ) for operating the gearbox. The gear shift device comprises a gear lever ( 15 ), a master cylinder ( 11 ) and a slave cylinder ( 12 ), which are connected to the gearbox ( 30 ). A hydraulic line ( 13 ) connects the cylinders ( 11, 12 ) with each other. The gear shift device also comprises a computer ( 40 ) which can receive information concerning an initiated gear shift operation, establish the value of a torque which is exerted on a drive shaft ( 21 ) between the vehicle&#39;s engine ( 20 ) and the gearbox ( 30 ), and control the engine&#39;s ( 20 ) power. In the hydraulic line ( 13 ) there is mounted a shut-off valve ( 42 ) and the computer ( 40 ) is arranged to transmit impulses for controlling the shut-off valve ( 42 ) based on the received information.

BACKGROUND OF THE INVENTION

The invention relates to a gear shift device for a vehicle.

A gear shift device of this type is known from U.S. Pat. No. 4,593,580.If the driving gear wheel is engaged with a first driven gear wheel andthe driving gear wheel requires to be disengaged from this driven gearwheel and the driving gear wheel requires to be engaged with a seconddriven gear wheel, the torque in the drive shaft is first reduced tozero, whereupon the driving gear wheel is brought out of engagement withthe first driven gear wheel. The drive shaft's frequency of rotation isthen matched to the frequency of rotation of a second driven gear wheelby means of a regulating device in such a manner that theircircumferential speeds are equal, whereupon the driving gear wheel isbrought into engagement with it.

Since the frequency of rotation of the driving gear wheel or the seconddriven gear wheel, or both of these gear wheels vary during the gearchange in order to achieve such a match, either due to the fact that theengine's power or the vehicle's speed and thereby the frequency ofrotation of the driven gear wheels are altered relatively quickly, theinterval in which a gear shift is possible may be very small. Since thevehicle's driver constantly exerts a force on the gear lever in order toachieve the gear shift, i.e. attempts are made to bring the gear wheelsinto engagement, a continuous sliding or scraping of the gear wheels'teeth against one another can easily occur before the frequencies ofrotation of the gear wheels have become matched to such an extent that agear change can take place. Furthermore, a fracture of teeth may occurif the gear wheels are engaged before their frequencies of rotation havebeen completely matched.

In manually operated gearboxes the displacement speed for the gear wheelwhich is moved by the slave cylinder during the engagement is a functionof the force which is exerted on the gear lever. Thus the gear shiftoperation may not be executed during the above-mentioned interval andthe gear wheels may slip or scrape against one another.

For example, if this force is great the gear shift may be performed tooquickly. If, on the other hand, the force is small, the result may bethat the gear shift operation is not started or completed within theabove-mentioned interval.

A hydraulic gear shift device with double-acting hydraulic cylinders isknown from the applicant's Norwegian patent NO 171426.

An object of the invention is to provide a gear shift device of the typementioned in the introduction, which to a far less extent is encumberedby the above-mentioned disadvantages.

SUMMARY OF THE INVENTION

In accordance with the foregoing object, this invention provides a gearshift device for a vehicle having a manually operated gearbox, aningoing drive shaft in the gearbox which is connected with an engine ofthe vehicle, an outgoing driven shaft from the gearbox, a hydraulic gearshift device which is connected to a selector device, the gearbox havingat least one driving gear wheel which is connected to the drive shaftand at least a first and a second, driven gear wheel which are connectedto the outgoing driven shaft and by means of the gear selector devicemay optionally be connected to the drive shaft, a computer which isconnected to (i) a gear shift operation-sensor device which is arrangedto establish the occurrence of a gear shift operation initiated by meansof the selector device and a gear into which a shift is to be made, (ii)a power control device for controlling the engine's power, (iii) atorque establishing device for establishing the value of a torque whichis exerted on the drive shaft, and (iv) frequency of rotation sensorsfor establishing the value of the frequency of rotation of the driveshaft and the driven gear wheels or the driven shaft respectively, thecomputer being arranged to receive impulses from the gear shiftoperation-sensor device, the torque establishing device and thefrequency of rotation sensors and to transmit control impulses to thepower control device, wherein said hydraulic gear shift device includesa master cylinder which is connected to said selector of the hydraulicgear shift device, a slave cylinder which is connected to a selectordevice of the gearbox, and at least one hydraulic line that connects themaster and slave cylinders with each other, and wherein the hydraulicgear shift device comprises a shut-off valve which is mounted in thehydraulic line, and the computer is arranged to transmit impulses forcontrolling the shut-off valve based on the received impulses.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic diagram of a gear shift device according tothe invention that illustrates the interconnection of the components ofthe device.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in the figure, the device according to the inventioncomprises a hydraulic gear shift device 10 with a double-actinghydraulic master cylinder 11, a double-acting hydraulic slave cylinder12 and two hydraulic lines 13, 14 connecting these cylinders with eachother.

It will be understood, however, that the cylinders may be single-actingand comprise return springs, in which case only one line extends betweenthe cylinders.

The master cylinder may be operated by means of a selector device, e.g.a gear lever 15, and the slave cylinder 12 may have an operating arm 16connected with its piston, which arm can be moved, for example,backwards and forwards as indicated by a double arrow.

The vehicle which is provided with the gear shift device comprises anengine 20 with a drive shaft 21. An end portion of the drive shaftextends into a gearbox 30 and a driving gear wheel 31 isnon-rotationally connected to this end portion. However, the drivinggear wheel may, for example, be moved along the drive shaft by means ofthe operating arm 16.

In the gearbox a number of driven gear wheels with different diametersare installed, only a first and a second driven gear wheel 32 and 33respectively being illustrated in the figure. The driven gear wheels 32,33 are arranged to rotate together with respective first and seconddriven gear wheel shafts 34, 35 which are rotatably mounted in thegearbox 30 and connected with an output shaft 36 which extends out ofthe gearbox. This output shaft 36 is connected in turn with drivingwheels of the vehicle (not illustrated).

When the driving gear wheel 31 is moved along the drive shaft 21 bymeans of the slave cylinder's operating arm 16, the driving gear wheel31 and thereby the engine's drive shaft 21 can be connected with eitherof the driven gear wheels 32, 33. By engaging the various driven gearwheels in this way, the object can be achieved that different torquesare exerted in the outgoing shaft 36 and different frequencies ofrotation obtained for it during constant engine power and frequency ofrotation of the drive shaft 21.

The gear shift device according to the invention comprises a computer40.

The computer is connected to:

a gear shift operation-sensor device S0 comprising a device S1 forindicating the initiation of a gear shift operation for example apressure sensor which detects the pressure of the hydraulic fluid in thecylinder chambers (not illustrated) of the double-acting master cylinder11, and which is arranged to establish the occurrence of a gear shiftoperation initiated by means of the selector device, i.e. the gear lever15. The gear shift operation-sensor device S0 may further comprise aselector device or sensor S2 for transmitting an impulse indicating towhich gear the shift has to be made.

The computer 40 is furthermore connected to:

a power control device P for controlling the power of the engine,

a torque establishing device T for establishing the value of a torquewhich is exerted on the input shaft, and

frequency of rotation sensors R1, R2, R3 for establishing the value ofthe frequency of rotation of the drive shaft 21 and the shafts 34, 35for the driven gear wheels 32, 33 respectively.

The torque establishment device T, may for example comprise sensors,such as strain gauges which are arranged to transmit to the computerimpulses corresponding to the torque in the drive shaft. Alternatively,this device may comprise sensors (not illustrated) which detect valuesfor, e.g., the engine's temperature and fuel consumption per time unittogether with the vehicle's speed and transmit corresponding impulses tothe computer. By means of these impulses the computer calculates a valuefor the torque which is exerted on the drive shaft 21.

Instead of the frequency of rotation sensors R2 and R3, a frequency ofrotation sensor R4 may be provided for establishing the frequency ofrotation of the driven shaft 36, the shafts 34, 35 for the driven gearwheels 32. 33 being constantly connected to the output shaft 36 androtating with a fixed gear ratio relative thereto. The frequency ofrotation sensor R4 therefore detects a frequency of rotation which isproportional to the frequency of rotation of the driven gear wheels.Such a gear ratio can be entered in the computer.

The computer is arranged to

receive impulses from the gear shift operation-sensor device S0, thetorque establishing device T and the frequency of rotation sensors R1,R2, R3 and possibly R4,

and to transmit control impulses to the power control device P in amanner which will be explained in more detail below.

In one of the hydraulic lines, for example the line 13, a two-positionshut-off valve 42 is inserted which may optionally be brought into afirst, open position, wherein hydraulic fluid can flow in the hydraulicline 13, or a second position wherein this fluid is prevented fromflowing in this line. This shut-off valve may be electrically operatedand is similarly controlled by the computer.

Furthermore, the hydraulic lines 13, 14 are connected to a double-actinghydraulic accumulator 44. The side of the hydraulic accumulator 44 whichis connected to the line 13 is connected to the portion thereof which islocated between the shut-off valve 42 and the master cylinder 11. Thehydraulic accumulator may comprise a cylinder part 46 wherein there ismounted a freely movable piston 48 which defines two cylinder spaces, ineach of which is mounted a compression spring 52, 54. These springs 52,54 attempt to centre the piston 48 in the cylinder part. A positionsensor A is arranged to establish the position of the piston in thecylinder part 46 and to transmit an impulse concerning this position,which indicates a ratio of charge for the accumulator, to the computer40.

The mode of operation for the gear shift device according to theinvention is as follows.

In the initial stage it should be assumed that a driven gear wheel, e.g.the gear wheel 32 which is connected to the frequency of rotation sensorR2, is engaged with the driving gear wheel 31, and that the shut-offvalve 42 is open.

If a gear shift is required, e.g. if the driven gear wheel 33 which isconnected to the frequency of rotation sensor R3 has to be engaged withthe driving (year wheel 31, an attempt will first be made to move thegear lever to the neutral position.

By means of this movement of the gear lever, the pressure of thehydraulic fluid in one cylinder chamber of the master cylinder 11 isincreased. The pressure sensor S1 immediately establishes this pressureincrease and transmits a corresponding impulse to the computer 40.

If in the course of this gear shift operation the driver has not reducedthe power, thus causing the torque in the drive shaft to be reduced toalmost zero, the computer 40 can effect a closure of the shut-off valve42 and transmit an impulse to the power device P, with the result thatit implements such a reduction of the engine's power. The force whichthe driver of the vehicle constantly exerts on the gear lever, however,also causes the hydraulic accumulator 44 to be charged, wherebyadvantageously the gear lever 15 may be be moved, thus giving the drivera satisfying feeling that the gear is being operated.

If the shut-off valve is closed and the torque in the drive shaft 21 hasbeen reduced almost to zero, the computer 40 causes an opening of theshut-off valve 42, whereupon the accumulator 44 quickly supplies fluidto the slave cylinder 12. Since the amount delivered may be great, theslave cylinder's piston and thereby the driving gear wheel are movedrapidly, with the result that the driving gear wheel is rapidly moved toa neutral position, wherein the driving gear wheel is not engaged withany driven gear wheel. For example a position sensor (not illustrated)can detect such a neutral position and transmit a corresponding impulseto the computer.

The gear selector sensor S2 then detects the desired gear as the gearlever is moved on past the neutral position, this sensor being mounted,for example, in the gearbox.

The shut-off valve 42 is then closed once again, whereupon the computer40 compares the frequencies of rotation for the driving gear wheel 31and the gear wheel 33 with which the driving gear wheel 31 is to beconnected.

If these frequencies of rotation are matched in such a way that thecircumferential speeds of these gear wheels agree or are within anacceptable differential speed range, the shut-off valve is opened,whereupon the gear lever can be moved to its final position for engagingthese gear wheels.

If the frequency of rotation of the driving gear wheel 31 is too low,the shut-off valve 42 remains closed and the computer 40 transmits animpulse to the power device P, thus enabling the engine's and therebythe driving gear wheel's frequency of rotation to increase.

If the frequency of rotation of the driving gear wheel 31 is too high,the power device P is controlled in such a manner that the engine'sfrequency of rotation is reduced.

When the circumferential speeds of the driving gear wheel 31 and of thedesired, driven gear wheel 33 have thereby approached each othersufficiently to allow the driving gear wheel 31 to be brought intoengagement with the desired, driven gear wheel 33, on the understandingthat the frequency of rotation of both gear wheels may hereby bealtered, the shut-off valve 42 is opened, thus enabling the hydraulicaccumulator 44 to deliver a large amount of hydraulic fluid rapidly tothe line 14 in order to ensure that the gear wheels 31, 33 are engagedin the course of the shortest possible time, i.e., while the frequenciesof rotation of the gear wheels are such that their circumferentialspeeds are within a fixed differential range, thus permitting anengagement of the gear wheels 31, 33 to take place without anunacceptable slipping or scraping of their teeth against one another.

After completion of the gear change, the power device P is giveninformation from the computer concerning an increase in the power to avalue corresponding to a selected accelerator pedal position or powervalue.

The shut-off valve 42 thereby assures a gear shift, by ensuring that thegear wheels of the gearbox which have to be brought into engagement,have obtained frequencies of rotation which match each other, thuspreventing a slipping of the gear wheels' teeth or a fracture thereof.

The hydraulic accumulator ensures that the gear lever can be moved in asubstantially smooth fashion during gearing, thus giving the driver ofthe vehicle a feeling that the gearing is being performed almostcontinuously even though the fluid flow in the lines 13, 14 istemporarily stopped, and that a large amount of fluid is delivered tothe slave cylinder for rapid operation thereof when the gear wheels ofthe gearbox which are to be brought into engagement during, gearing havefrequencies of rotation which are within the limits which ensure thatgearing takes place noiselessly and without causing damage.

In the above a simplified embodiment of a gearbox has been described. Itwill be appreciated that the gearbox may be designed in other ways. Forexample, it may comprise several driven gear wheels for each gear.Moreover, the drive shaft may be in the form of a toothed shaft, formingthe driving gear wheel with which driven gear wheels can be brought intoengagement.

In addition to the above-mentioned advantages of the arrangement of theshut-off valve, it can also prevent an inadvertent shift to a reversegear while the vehicle is moving forwards. Moreover, it can prevent aninadvertent shift to a gear which is not an adjacent gear to the gearwhich is engaged for example a gear which is too low, whereby the enginemay be damaged.

Even though the gear shift device according to the invention has beendescribed above in connection with a gearbox without a synchronisingdevice, it will be understood that the gear shift device may also beemployed for gearboxes with a synchronising device, if this should bedesirable, e.g. for certain technical reasons during production or inorder to obtain a synchronised gearbox whereby the vehicle's driver doesnot need to exert great force while changing gear.

Even though it has been stated above that the gear shift device ishydraulic, it will be understood that it may be, e.g., electricalinstead. In this case the hydraulic master cylinder and slave cylinderare replaced by an electrical transmitter device or a slave device. Thehydraulic shut-off valve 42 is replaced by an electrical device whichprevents operation of the slave device in the same way as in thehydraulic gear shift device.

What is claimed is:
 1. A gear shift device for a vehicle comprising amanually operated gearbox, an ingoing drive shaft in the gearbox whichis connected with an engine of the vehicle, an outgoing driven shaftfrom the gearbox, a hydraulic gear shift device which is connected to afirst selector, the gearbox having at least one driving gear wheel whichis connected to the drive shaft and at least a first and a second,driven gear wheel which are connected to the outgoing driven shaft andby means of the first selector may optionally be connected to the driveshaft, a computer which is connected to (i) a gear shiftoperation-sensor device which is arranged to establish the occurrence ofa gear shift operation initiated by means of the first selector and agear into which a shift is to be made, (ii) a power control device forcontrolling the engine's power, (iii) a torque establishing device forestablishing the value of a torque which is exerted on the drive shaft,and (iv) frequency of rotation sensors for establishing the value of thefrequency of rotation of the drive shaft and the driven gear wheels orthe driven shaft respectively, the computer being arranged to receiveimpulses from the gear shift operation-sensor device, the torqueestablishing device and the frequency of rotation sensors and totransmit control impulses to the power control device, wherein saidhydraulic gear shift device includes a master cylinder which isconnected to said first selector of the hydraulic gear shift device, aslave cylinder which is connected to a second selector of the gearbox,and at least one hydraulic line that connects the master and slavecylinders with each other, and wherein the hydraulic gear shift devicecomprises a shut-off valve which is mounted in the hydraulic line, andthe computer is arranged to transmit impulses for controlling theshut-off valve based on the received impulses.
 2. The gear shift deviceof claim 1, wherein a hydraulic accumulator is connected to thehydraulic line.
 3. The gear shift device of claim 1, wherein the mastercylinder and the slave cylinder are double-acting and between them thereextend two hydraulic lines, the shut-off valve being mounted in one ofthese lines.
 4. The gear shift device of claim 2, wherein the mastercylinder and the slave cylinder are double-acting and between them thereextend two hydraulic lines and the hydraulic accumulator isdouble-acting and connected to both the lines.
 5. The gear shift deviceof claim 2, wherein the hydraulic accumulator is connected to a chargecondition sensor for establishing the hydraulic accumulator's chargecondition, and which is connected to the computer.
 6. The gear shiftdevice of claim 1, wherein the gear shift operation-sensor devicecomprises a pressure sensor for establishing a pressure of hydraulicfluid in the hydraulic line.
 7. The gear shift device of claim 3,wherein the gear shift operation-sensor device comprises two pressuresensors for establishing a pressure of hydraulic fluid in the respectivehydraulic lines.
 8. The gear shift device of claim 1, wherein themanually operated gearbox does not have a mechanical synchronisationdevice.
 9. The gear shift device of claim 1, wherein the first selectorof the hydraulic gear shift device is a gear lever.